It is known that sources of electromagnetic radiation vary as regards output intensity vs. wavelength. Further, it is known that detectors of electromagnetic radiation become saturated when too high an intensity is input thereto. Where the intensity of one or more a wavelengths in a spectrum of wavelengths is high enough to saturate a detector, one approach is to attenuate the intensity of all wavelengths. This can be accomplished by a Neutral density filter, but neutral density filters do not pass UV wavelengths. Problems develop using this approach in that reducing the intensity of the highest intensity wavelengths can cause reduction of the intensity of other wavelengths below that which a detector can detect. Another approach to reducing intensity is to pass a beam of electromagnetic radiation through an iris which can be reduced in opening size, however, non-uniformity in the beam can lead to non-uniform results.
It is also disclosed that ellipsometers and polarimeters and the like typically comprise a source of a beam of electromagnetic radiation, a beam polarizer, an analyzer and a detector arranged so that a beam provided by the source passes through the polarizer, impinges on a sample and the passes through he analyzer and into the detector. The beam polarizer sets a polarization state in said beam which is changed by interaction with a sample, and the analyzer selects polarization states which are passed to the detector.
Conventional practice of ellipsometry involves directing a polarized beam of electromagnetic radiation, which can be focused or not, at a sample surface at a set angle of incidence, and detecting the resulting electromagnetic radiation after its interaction with the sample with a detector. Change in polarization state of the beam provides insight into the sample composition. Typically there is no need to consider that the beam leaving a sample might not be sufficiently intense for a detector to detect, or that it might be so intense, at least at one or more wavelengths in a spectroscopic range of wavelengths, that the detector becomes saturated. However, when applying ellipsometry to samples which do not uniformly reflect specularly, such as new generation solar cells, these concerns become very important. The present invention focuses on adjusting ellipsometer systems to “optimize” signal detection when “difficult” samples are investigated, rather than on setting parameters, such as angle of incidence and beam focusing based on some other criteria.
Patents identified which include the terms “solar cell” and “ellipsometry” or “ellipsometer” were identified and are:
U.S. Pat. Nos. 7,282,798; 7,238,596; 7,235,735; 7,235,154; 7,227,196; 7,224,527; 7,202,143; 7,187,443; 7,164,077; 7,161,173; 7,160,809; 7,144,303; 7,141,489; 7,130,055; 7,125,926; 7,049,004; 7,020,372; 7,005,669; 6,961,499; 6,946,161; 6,911,349; 6,885,458; 6,885,444; 6,819,845; 6,812,047; 6,777,706; 6,738,139; 6,722,140; 6,716,656; 6,710,366; 6,662,570; 6,620,631; 6,613,697; 6,593,077; 6,521,826; 6,498,380; 6,444,8.98; 6,359,973; 6,362,414; 6,300,141; 6,200,825; 6,165,875; 6,124,545; 6,080,683; 6,049,220; 5,821,171; 5,418,019; 5,221,364; 5,131,752; 5,011,706;U.S. Pat. No. 7,226,966; 7,039,556; 7,011,871; 6,855,369; 6,407,327; 6,297,134; 6,156,967; 5,903,047; 5,246,782, 4,563,367; 4,434,025;
Published Patent Applications identified which include the terms “solar cell” and “ellipsometry” or “ellipsometer” were identified and are:
20080022896; 20070232782; 20070228364; 20070202123; 20070190305; 20070157966; 20070128370; 20050288896; 20050227465; 20050195486; 20050189015; 20050187411; 20050186495; 20050184287; 20050199238; 20050052119; 20050022863; 20040186216; 20030178057; 20030031438; 20020053395; 20010005554;20080032602; 20080015269; 20070258147; 20070241670; 20070235133; 20070232065; 20070227586; 20070221914; 20070172978; 20070006915; 20070004220; 20070001151; 20060276047; 20060231827; 20060209566; 20060174935; 20060108688; 20050150599; 20050106713; 20050022863; 20050012095; 20040259353; 20040186216; 20040103937; 20040062945; 20040058468; 20040058079; 20030087471; 20030087121; 20030027433; 20010025649; 20010013361.
As the system of the present invention includes crossed-polarizers, patents identified which include the terms “crossed-polarizer” and “ellipsometry” or “ellipsometer” were identified and are:
U.S. Pat. Nos. 7,236,221; 7,221,420; 7,211,304; 7,163,724; 7,083,835; 7,061,561; 6,934,024; 6,798,511; 6,693,711; 6,112,114; 5,787,890; 5,303,709; 4,097,110; 7,170,574;
2006/0215158; 2006/0203164; 2006/0193975; 2005/0286001; 2005/0270459; 2005/0270458; 2005/0024561; 2004/0189992; 2004/0179158; 2003/0227623; 2003/0227623; 2002/0091323; 2006/0141466; 2006/0115640; 2006/0099135; 2005/0270458; 2005/0128391; 2004/0208350; 2004/0189992; 2003/0227623; 2002/0091323.
It is believed that the foregoing identified prior art is the most relevant to be found and has as its major thrust the application of conventional ellipsometry to the measurement of various parameters such as common to solar cells. Even in view of the prior art, however, need remains for improved systems and improved methodology which better enable application of ellipsometry to the investigation of sample characterizing parameters of samples which demonstrate low specular reflectance and/or which are depolarizing, via, on a case by case basis, controlling selection(s) from the group of: intensity, focus, and angle of incidence of a beam of spectroscopic electromagnetic radiation used to investigate said materials.